The use of an exercise apparatus in order to exercise for physical therapy purposes or to exercise for diagnostic and rehabilitation purposes is known. A representative patent is U.S. Pat. No. 4,452,447 which issued to the assignee of the present invention and was directed to an ankle exerciser adapted for permitting isokinetic exercise of the ankle joint of the user. The apparatus provided for movement about three mutually perpendicular axes with each axis of movement having a double-action hydraulic cylinder associated therewith in order to permit selected resistance to motion about that axis. This apparatus, although originally believed to permit free movement of the ankle joint, resulted in some binding thereof since the three mutually perpendicular axes of movement were not colinear with the natural axes of the foot or ankle. The result was an apparatus which was not entirely satisfactory with respect to its intended purpose.
Also, it should be understood that other ankle exercise apparatus are known which provide for exercise of the ankle joint for rehabilitation purposes including the ORTHOTRON II manufactured by Lumex, Inc. of Ronkonkoma, N.Y. This apparatus provides for plantar flexion and dorsiflexion movement of the foot about the axis of the ankle joint against a rotary actuator-type resistance means having a rotational axis in alignment or colinear with the ankle axis with the foot properly positioned in the foot plate mechanism of the exercise apparatus. This apparatus allows ankle joint exercise with the user in prone position or in supine position with the knee flexed.
The CYBEX II apparatus, also manufactured by Lumex, Inc. of Ronkonkoma, N.Y., is a commercial system for measurement of isolated joint movement and functional capabilities of the ankle joint. The apparatus provides for independent exercise and measurement of the ankle joint during plantar flexion and dorsiflexion motion and of the subtalar joint of the foot during inversion and eversion motion. However, this apparatus is understood to utilize only a single rotary resistance means so as to require separate and distinct tests to evaluate the ankle joint or other joints of interest. The CYBEX II apparatus does provide for colinear alignment of the rotary resistance means axis with the axis of the ankle joint or other joint to be tested or exercised.
Also of possible interest is the MULTIAXIAL ANKLE EXERCISER manufactured by Multiaxial, Inc. of Lincoln, R.I. Unlike apparatus which provide for evaluation of the performance of a joint or joints of interest, this apparatus essentially is an ankle exercise apparatus comprising a foot plate with associated straps to secure the foot thereto and pivotally secured to the top of a pedestal for universal and multiaxial movement against an adjustable resistance. The ankle exercise apparatus, although providing for complex combinations of movements against a predetermined resistance, does not utilize either independent resistance means for each axis of movement or the hydraulic rotary actuator-type resistance means utilized in the instant invention. This apparatus is not believed capable of providing meaningful performance evaluation of the ankle joint or subtalar joint but merely provides for exercise of the foot about a plurality of axes including the axes of the ankle joint and the subtalar joint.
In summary, it is believed that known foot and ankle joint exercise apparatus are not entirely satisfactory to analyze performance of the subtalar joint and the ankle joint. Moreover, it is believed that none of the prior art machines provide for a hydraulic resistance means to be associated with movement about both the ankle and subtalar joint axes and which have rotational axes colinear with both the pivotal axes of the subtalar joint and the ankle joint so as to accommodate natural movement of the foot and ankle during exercise and/or performance evaluation.